The present invention relates to motor vehicle sensors and actuators.
Modern motor vehicles are equipped with numerous sensors which provide detailed information regarding the operation of the vehicle. This information may be displayed for a driver or it may be processed and provided to various vehicle control systems. A target wheel sensor, for example, may be used to determine the angular speed or angular position of a rotating part in the vehicle, e.g., a crankshaft and a driveshaft. In either case, a target wheel may be engaged with the rotating part for inducing signals in one or more sensors positioned next to the target wheel, with the signals representing the angular position or angular speed of the rotating part. These signals can be used in various control systems, e.g., an ignition system and a speed control system.
The present invention recognizes that certain applications require the detection of not only the position of the target wheel, but the detection of the direction of motion of the target wheel as well. Devices have been provided that can be used to detect the position of the target wheel and the direction of motion. These devices typically require a first sensor and a second sensor placed at a predetermined angular distance from each other around a target wheel. Unfortunately, the need for a second sensor increases the cost of the device.
The present invention has recognized these prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies.
A target wheel sensor assembly includes a sensor and a target wheel that is placed in close proximity to the sensor so that it is sensed by the sensor. The target wheel is configured so that as it rotates, it causes the sensor to output an asymmetric signal. In a preferred embodiment, the target wheel alternatingly forms plural teeth and plural slots. The teeth are configured so that they cause the sensor to output an asymmetric signal as the target wheel rotates.
Preferably, the sensor defines a bottom and each tooth forms a flat portion that is parallel to the bottom of the sensor. Each tooth also forms a chamfered portion that is contiguous to the flat portion. The chamfered portion forms an angle, xcex1, with the bottom of the sensor. In a preferred embodiment, the angle, xcex1, is between ten degrees and thirty degrees.
Preferably, the sensor defines a width and each tooth and slot define a pitch. In a preferred embodiment, the ratio of the slot width to the pitch is between 0.3 and 0.9. To ensure that the waveform of the signal output by the sensor is never close to zero, the ratio is between 0.4 and 0.7. Moreover, to yield a significant flux variation the ratio is between 0.7 and 0.9.
In another aspect of the present invention, a target wheel sensor assembly includes a target wheel and one and only one sensor placed in close proximity to the target wheel. The sensor senses the position of the target wheel and the direction of motion of the target wheel.
In still another aspect of the present invention, a system for determining the direction of rotation of a rotating target wheel includes a target wheel and a sensor placed in close proximity to the target wheel. As the target wheel rotates, the sensor outputs an asymmetric signal. This aspect of the present invention includes a circuit that is connected to the sensor. The circuit receives the asymmetric signal and detects different positive and negative peaks of the asymmetric signal to determine the direction of motion of the target wheel.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: